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TECHNICAL REPORTS

Methane Oxidation in an Intensively Cropped Tropical Rice Field Soil under Long-Term Application of Organic and Mineral Fertilizers

^a Laboratory of Soil Microbiology, Div. of Crop Production, Central Rice Research Institute, Cuttack, Orissa, India
^b School of Geography and Geology, McMaster Univ., Ontario, ON L8S4K1, Canada

^* Corresponding author (adhyas{at}yahoo.com).

Received for publication November 15, 2006. Methane (CH₄) oxidation is the only known biological sink process for mitigating atmospheric and terrestrial emissions of CH₄, a major greenhouse gas. Methane oxidation in an alluvial soil planted to rice (Oryza sativa L.) under long-term application of organic (compost with a C/N ratio of 21.71), and mineral fertilizers was measured in a field-cum-laboratory incubation study. Oxidation rates were quantified in terms of decrease in the concentration of CH₄ in the headspace of incubation vessels and expressed as half-life (t) values. Methane oxidation rates significantly differed among the treatments and growth stages of the rice crop. Methane oxidation rates were high at the maximum tillering and maturity stages, whereas they were low at grain-filling stage. Methane oxidation was low (t = 15.76 d) when provided with low concentration of CH₄. On the contrary, high concentration of CH₄ resulted in faster oxidation (t = 6.67 d), suggesting the predominance of "low affinity oxidation" in rice fields. Methane oxidation was stimulated following the application of mineral fertilizers or compost implicating nutrient limitation as one of the factors affecting the process. Combined application of compost and mineral fertilizer, however, inhibited CH₄ oxidation probably due to N immobilization by the added compost. The positive effect of mineral fertilizer on CH₄ oxidation rate was evident only at high CH₄ concentration (t = 4.80 d), while at low CH₄ concentration their was considerable suppression (t = 17.60 d). Further research may reveal that long-term application of fertilizers, organic or inorganic, may not inhibit CH₄ oxidation.

Abbreviations: cfu, colony forming unit • sMMO, soluble methane monooxygenase • SOM, soil organic matter • SSP, single superphosphate • NRN, Ninhydrin reactive nitrogen • TOC, total organic carbon • TTC, tri-phenyl tetrazolium chloride • WHC, water holding capacity